1. Field of the Invention
The invention relates generally to providing of downstream and upstream data connectivity. More specifically, the invention relates to an interface that allows the extension of a cable modem data service over wireless links.
2. Discussion of the Prior Art
The delivery of data using the cable television (CATV) system has become common in residential areas where CATV is commonly available. The data are delivered both downstream and upstream using available channels and/or frequencies. The end user can connect to such systems through a cable modem that is capable of delivering the downstream data respective of a specific user to that user, as well as sending upstream data sent from the user and that are intended to reach another node of the system.
Because providers of CATV expect to deliver additional services, such as data for Internet connectivity, there is an interest to serve as large as possible number of clients. However, it is not always possible to provide a direct connection to each location. For example, a shopping mall near a residential area is not commonly wired for the use of CATV because to do so is quite low. FIG. 1 is a diagram showing the distribution of CATV to a residential area. Clients use a cable modem to have access to downstream data and to transfer data upstream. If the CATV operator wants to provide a service to clients in the shopping mall, a distribution coax cable must be laid. This includes a significant cost.
Some cable modems are compliant with the Data Over Cable Service Interface Specifications (DOCSIS), which interface specifications for standard, interoperable, data-over-cable network products, the standard specifications of which are herein incorporated by this reference thereto. Internet Service Providers (ISPs) using Multipoint Microwave Distribution System (MMDS) may also be compatible with DOCSIS. However, current thereto MMDS networks are not entirely satisfactory. MMDS networks are characterized by the limited number of channels available in the low radio frequency (RF) bands. Only 200 MHz of spectrum (between 2.5 GHz and 2.7 GHz) is allocated for MMDS use. This constraint reduces the effective number of channels in a single MMDS system.
Moreover, the MMDS wireless cable uses 6 MHZ television channels for upstream and downstream transmission. These channels are relatively closely spaced in frequency. Because the channels are so closely spaced in frequency, a diplexer is required at each subscriber location to separate the upstream transmission path and the downstream receive path. Thus, the processing equipment required, including the diplexer, is relatively expensive and cumbersome. Also, the up to two 6 MHZ channels which may be allocated to the reverse direction are less than the full upstream capacity of DOCSIS. This is a significant bandwidth limitation. In addition, because the MMDS channels are licensed, the ISP must go to the expense of purchasing or leasing a license that could cost in the millions of dollars.
Fortunately, in 1997 the U.S. Federal Communications Commission (FCC) set aside 300 MHz of spectrum in the 5 GHz band for the U-NII service. Three bands are defined in this spectrum: 5.15 to 5.25 GHz (U-NII band 1) and 5.25 to 5.35 GHz (U-NII band 2), which are designated for wireless LAN and other shorter-range use; and 5.725 to 5.825 GHz (U-NII band 3) for wide-area networking that reaches a greater distance with higher power. The U-NII bands are designated for wideband, high-data-rate digital communications. They are also license-free i.e. no license is required to operate on the U-NII bands. A detailed description of a system overcome the above discussed limitations, and that exploits the license free bands is provided in U.S. patent application Ser. No. 10/282,533, titled System and Method for Wireless Cable Data Transmission, assigned to common assignee and which is hereby incorporated by reference for all that it contains.
Systems that is known for using a cable modem at 5.8 GHz, as well as other microwave frequency bands, are quite complex. The downstream may use a single down conversion in the customer premises equipment (CPE) prior to the cable modem, with a separate local oscillator and phase locked loop (PLL). The CPE upstream requires a dual conversion architecture with two additional local oscillators and PLLs. To employ the benefits of a block up conversion in the CPE upstream, additional filter stages are required. Alternatively an individual channel conversion is employed for the upstream, which then also requires PLL programming to adjust for the changing cable modem upstream output frequency. Furthermore, the prior art uses a high-pass/low-pass filter combination, with multiple circuit elements. This results in high complexity and fabrication difficulty when used in conjunction with a flat panel antenna.
It would therefore be advantageous to provide an apparatus and a method that allows a CATV operator to deliver a data service to areas that are in the proximity of the service area, but that are not currently reached by a distribution coax cable. It would be further advantageous if such a system would not require additional transmission licenses. It would be further advantageous if a proposed implementation overcomes the deficiencies of prior art solutions by using a single PLL.